A couple of suggestions

Hi Scott,

I did an inspection today of an RV12 SLSA. Everything looks great and you guys did a nice job with the engine systems and hoses.
I do have a couple of suggestions for the company assembling these.

1. Safety wire the oil magnetic plug.
2. Safety wire the oil pressure plug screw just below and to the left of the oil filter on the bottom.
3. Safety wire the exhaust springs.
4. Don't fill the exhaust springs with silicone. We discuss this in some classes. When you fill them the springs retain heat and can prematurely fail. When left empty they have air circulation for some heat dissipation. Rotax recommends the high temp RTV to be placed on the outside of the exhaust spring. A small pencil thin bead isn't strong enough to do a good vibration dampening job. Making it about 3/8" (up to 1/2") wide by about 1/8" (up to 1/4" thick and working it in between the coils does a great job of letting heat dissipate, dampening vibration and allows you to pass the safety wire down through the center of the exhaust spring.
5. Don't over tighten the carb throttle arm cable nut. This plane had wire throttle cable trands cut.
6. Don't cut the throttle cable too short leave it about 2" past the throttle arm attachment so you have some room to adjust the cable length if need be or trim the end of the cable if it frays. This plane had its cable trimed right up at the throttle arm screw.
7. Use a clear plastic line off the fuel pump drain. You have a nice aluminum line, but you'll never really know if the pump is oozing or has a slow leak unless you get down to the bottom of the tube and find an oily tip which might not happen due to a slow ooze and or the air blowing it off the tube tip. The clear line allows an owner to see an oozing fuel pump in a second.


Nice aircraft and the owner was very happy with it and whom ever set the prop rpm did a nice job by not over pitching the prop. It had really good performance.

Maybe this is a dumb question, but if you safety wire the spring by passing a wire down the centre, through the lugs and then tightening it up, isn't that going to inhibit the movement of the spring? Or do you leave the wire loose?

You pass a folded piece of wire over the top spring loop and down through the center and then out the bottom. You give that a few twist the pass it over the bottom spring loop and twist it. You are not trying to tighten the wire. It should be just a tad loose. The wire doesn't hold the spring or joint in place it is only there so if the spring breaks you keep all pieces. I highly recommend you use .041 wire. Others tend to break.

OK that makes sense. Thanks for the explanation.

How about a picture.

Please post a picture if you can of the spring with safety wire on it. Thanks.

Rotax exhaust spring safety wire and RTV

Here is a pic I have had for a while. You cab see the gaps in the spring coil. Work or just press the RTV into and between the coils. It will dampen the vibration.


(It got turned into a video instead of a picture. Just pause it half way through)


http://www.youtube.com/watch?v=I6Y2_8CXFI0&feature=youtu.be

I was surprised too that several items on the engine were not safetied from the factory. After all there was a factory test run. No big deal, just something for a builder to look for at installation.

Thanks for the complements on the RV-12 Roger. Glad you liked the airplane, and your feedback is appreciated. One general comment though, is that designing an airplane has many challenges. Particularly in areas were we are using something new to us (like the Rotax engine was when we started this 5 years ago). In that case, it is likely that most of the time we will defer to recommendations/procedures specified by the manufacturer (though there are exceptions)

Other reply comments are in red.

roger lee said:

Hi Scott,

1. Safety wire the oil magnetic plug.
2. Safety wire the oil pressure plug screw just below and to the left of the oil filter on the bottom.

I admit that safety wiring these may be a good idea (at least not a bad one). They are not done because the Rotax factory doesn't seem to think it is necessary (doesn't come from the factory that way and there is nothing in any of the documentation specifying that it be done). Interestingly enough, there are numerous other items on the engine in which there is no means of safetying.

3. Safety wire the exhaust springs.
These springs don't get safety wired because it is not a pusher aircraft. Interestingly enough, if the springs are wired as recommend by Rotax in the installation manual, it still doesn't assure they will be captured in case of breakage.

4. Don't fill the exhaust springs with silicone. We discuss this in some classes. When you fill them the springs retain heat and can prematurely fail. When left empty they have air circulation for some heat dissipation. Rotax recommends the high temp RTV to be placed on the outside of the exhaust spring. A small pencil thin bead isn't strong enough to do a good vibration dampening job. Making it about 3/8" (up to 1/2") wide by about 1/8" (up to 1/4" thick and working it in between the coils does a great job of letting heat dissipate, dampening vibration and allows you to pass the safety wire down through the center of the exhaust spring.

Once again, this directly conflicts with the Rotax Installation Manual. The most recent release 912 Installation Manual (AUG. 2012) specifically says to fill the springs.


5. Don't over tighten the carb throttle arm cable nut. This plane had wire throttle cable trands cut.

I will pass along the comment.

6. Don't cut the throttle cable too short leave it about 2" past the throttle arm attachment so you have some room to adjust the cable length if need be or trim the end of the cable if it frays. This plane had its cable trimed right up at the throttle arm screw.

If the cable is left with an additional 2 inches, it can interfere with portions of the engine that are ahead of the carb's, and prevent the throttle from opening fully.

7. Use a clear plastic line off the fuel pump drain. You have a nice aluminum line, but you'll never really know if the pump is oozing or has a slow leak unless you get down to the bottom of the tube and find an oily tip which might not happen due to a slow ooze and or the air blowing it off the tube tip. The clear line allows an owner to see an oozing fuel pump in a second.

I believe using clear plastic tubing directly connected to the fuel pump would directly conflict with the installation recommendations in the Rotax documentation (but I didn't go back and double check this one).

Click to expand...

Hi Scott,

Starting on the last comment.
Rotax sends clear plastic tubing in some of their fuel pump boxes. I just got 4 of them and they all had clear plastic tubing. I was doing a good pre-flight today and found my new pump had an internal leak. The pump has 100 hrs. and is 1 year old. I only found it because of the fluid and discoloration in the line.

There are several things on a Rotax engine from the factory that are not done and left up to the installer, but doesn't mean they shouldn't be done. You will find in the field and when classes are taught that we recommend the oil plug and fuel pressure screw be safety wired. They have holes already drilled for this. The manuals are are not 100% for procedures.

The springs whether a pusher or not should be safety wired as explained in bulletins and in the Installation manual and it doesn't specify pusher or tractor. Depending on how you wire them it can help with vibration. It may not be a pusher, but were do you think those broken springs are going to end up. On the runway, taxiway and falling from a plane over homes and people.
Using .041 wire and wiring like the picture and leaving the wire loose will guarantee the springs will stay with the plane. After many years of doing this I get to see all those broken springs. Other Mfg's safety these and they all believe there is a good reason. Nothing to loose by doing it and everything to gain.

Filling the springs with silicone is old school that should have been changed and isn't really taught any more because of the heat retention and premature failure rate. I had this discussion a few years back and went right to Rotax. The answer was use it on the outside. Unfortunately it takes years sometimes to get things changed.

2" of extra cable length doesn't interfere with the throttle arm operation and leaving it cut right up by the throttle arm may guarantee and complete cable replacement if they need more. I haven't seen any other throttle cables from any other Mfg this short and I work on all LSA's and get to offer suggestions on a regular basis.
The RV12 SLSA I just did the 25 hr. on had to have that cable replaced. The 2" was left on and offers no issue, but now the cable can be trimmed for frayed ends when the cable needs to be removed from its attachment screw. If the cable had to be pulled from this attachment screw now there was no way it would ever go back through the hole because it was crushed and frayed. If you leave it a little longer you can trim it when needed.
___________________________________________________________________________________________
Here is an email from Rotax on the springs:
The book is out dated on the silicone application.

"Hello again Roger

Springs for the exhaust, the question comes up from time to time, and as always speculation of the correct way is based on some misunderstanding of the function and purpose of the practice of silicone application. Silicone, high temp in this application, is used to dampen the vibrations that can lead to the premature breakage of the spring when it is in normal use.

Reasons for breaking are varied but overstretching, (attachment of the spring tang to the pipe and muffler too wide) and using a tool that leaves a mark on the spring are the most common. Always pull the spring on with a spring tool, do not use pliers, cutters, or any tool that is able to leave a mark in the spring. Lets remember that the material is heat treated after it is twisted. Any mark creates a weak spot in the wire.

The idea of safety wire on the spring also has to be considered, it too can create a problem. When you wire the spring you have some options, I prefer to wire from eyelet to eyelet and pass inside the spring, you must leave a small amount of slack in the wire, unlike any other time you do safety wire. The reason is simple, we have to allow for some moment of the joint, otherwise the wire can break.

Now, the silicone as discussed has to dampen vibration, so it only needs to cover the spring in a small area. The correct method is to draw a bead over the top of the spring, NO MORE THAN 1/4 to 3/8 INCH wide. I like to start from one spring tang, draw the bead from there, starting at one contact end of the safety wire, go across the top of the spring and to the other spring tang. This will deaden the wire vibration, and it will capture the small spring loop at each end should the wire break.

HEAT, it something that we have to consider, if you do not allow the spring to breathe, to cool, it may overheat and fail prematurely. So the idea is to leave the spring to move and to cool with the air, we do not want to stop the spring movement or from keeping cool.

I hope that this long winded explanation helps, your free to pass it on."

______________________________________________________________

No matter what, it's still a nice aircraft and I hope it does well.

roger lee said:

Here is an email from Rotax on the springs:
The book is out dated on the silicone application.

"Hello again Roger

Springs for the exhaust, the question comes up from time to time, and as always speculation of the correct way is based on some misunderstanding of the function and purpose of the practice of silicone application. Silicone, high temp in this application, is used to dampen the vibrations that can lead to the premature breakage of the spring when it is in normal use.

Reasons for breaking are varied but overstretching, (attachment of the spring tang to the pipe and muffler too wide) and using a tool that leaves a mark on the spring are the most common. Always pull the spring on with a spring tool, do not use pliers, cutters, or any tool that is able to leave a mark in the spring. Lets remember that the material is heat treated after it is twisted. Any mark creates a weak spot in the wire.

The idea of safety wire on the spring also has to be considered, it too can create a problem. When you wire the spring you have some options, I prefer to wire from eyelet to eyelet and pass inside the spring, you must leave a small amount of slack in the wire, unlike any other time you do safety wire. The reason is simple, we have to allow for some moment of the joint, otherwise the wire can break.

Now, the silicone as discussed has to dampen vibration, so it only needs to cover the spring in a small area. The correct method is to draw a bead over the top of the spring, NO MORE THAN 1/4 to 3/8 INCH wide. I like to start from one spring tang, draw the bead from there, starting at one contact end of the safety wire, go across the top of the spring and to the other spring tang. This will deaden the wire vibration, and it will capture the small spring loop at each end should the wire break.

HEAT, it something that we have to consider, if you do not allow the spring to breathe, to cool, it may overheat and fail prematurely. So the idea is to leave the spring to move and to cool with the air, we do not want to stop the spring movement or from keeping cool.

I hope that this long winded explanation helps, your free to pass it on."

______________________________________________________________

Scott I hope this helps some and I know your answer came from someone else.

No matter what, it's still a nice aircraft and I hope it does well.

Click to expand...

Not sure what the "I know your answer came from someone else." statement means? I wrote it. It was my words.

Anyway, Your feed back amplifies how difficult this whole process is. We used the Rotax documentation to try and do it right but then get told it is wrong, don't do that. BTW, the way the diagram in the install manual for safety wiring the springs shows to do it also doesn't match the way you are describing.

I am Rotax Service, and Maint. certified. I have been to renewal classes. I have never heard an instructor at a class say "don't put silicone inside the springs"
Are you willing to share who the author of the e-mail from Rotax was, so that I can follow up with them (feel free to Private Message me if you prefer)?

Another challenge is that Aric Tucker and someone from Lockwood aviation did an audit on the RV-12 FWF installation a few years ago at Sun & Fun. They had a couple of minor suggestions that were implemented, but said that over all it looked well engineered. Most importantly, they made no mention of any of the things you have commented on, and other than changes that have been implemented since then (new style fuel pump with drain line, etc.) what you saw is exactly like what they saw.

Hi rvbuilder,

Sorry about the last comment about "coming from someone else". I thought that came from Scott and it was my failure to notice it came from you.
Sorry

The problem has been Rotax does change its mind once in a while when they get enough experience that something works better than another and there are a few typos in the manual, too. Part of the problem is they don't keep up fast enough for manual updates. Kind of like when they used to say turn the idle stop screw counterclockwise to increase rpm. That took years to change.

I think the RV12 SLSA is a very good plane and would tell anyone that.
I fully agree that some times installs or keeping up with something new can be tough and of course sometimes there is more than one way to do something and either way is good. One reason you may not have heard that was possibly someone didn't ask, the instructor forgot and sometimes they have personal preferences.
My comments were just suggestions to help out and some are not hard and fast rules, just some things to make it easier on the owner or mechanic. I have been doing this for a number of years and annual at least 30 Rotax 912's a year, plus all the little maint. repairs along the way.

The diagram in the Installation manual for the spring safety wire is a suggestion to help dampen the vibration, but won't retain the spring if it breaks on the hook shank. The other way (in the picture) retains the complete spring. Some things I may copy and paste something sent to me in writing I'm ask not to throw names out, but I am happy to tell you on the phone and even discuss and bat these ideas around some.

Give me a call anytime. I'm sure we may be able to help each other from time to time.

Roger
520-574-1080 home
520-349-7056 cell

I leave for Page, AZ tomorrow morning for the Fly-In I sponsor. Your welcome to call anytime this week, but after 12 noon would be easier to reach me on my cell. We fly out each morning to different locations in the mornings.

Hi Scott,

Another thought on the aluminum drain for the pump. To make it so an owner could have a quick check when the cowl is off is to make the first 6"-8" clear plastic and then go aluminum. This would give the owner a nice quick visual check.


p.s.
I was a little confused on who was who here on the forum with names. Must be old age creeping up. I have been straightened out.

Exhaust springs, RTV & safety wire

Roger and Scott,

Good info in the discussion about springs etc. As I am finishing up my RV-12, this is a subject that has now come up for me. I am wondering what the current thinking is on the subject. It has been a little while since this was last discussed.